Applications exist, particularly in the field of neurosurgery, for mechanisms capable of effecting accurate positioning of an implement, such as the working end of a surgical instrument, an electrode, a needle, or the like. Because the implement must be spatially moved to any desired position over the skull of the patient, the mechanism for effecting this positioning must be capable of multiple movements in a three dimensional coordinate system. Consequently, sliding movements with respect to a fixed rail over the operating table, coupled with rotational movements, tilting movements and the like, all must be precisely controlled in order to place the implement at the desired position and angle at which it is to be used.
Mechanisms for positioning such implements typically require a number of separate adjustments, with separate locking of each of the different movements necessary to effect and hold the three-dimensional positioning. As a result, such mechanisms are difficult and cumbersome to use and require substantial skill and considerable manipulation on the part of the physician or other user.
Three surgical instrument positioning devices, capable of multiple movement in a three dimensional coordinate system, are disclosed in the U.S. patents to Mocarski No. 3,073,310; Moore No. 4,723,544; and Carol No. 4,955,891. The devices disclosed in each of these patents are relatively complex arrangements of rotational and sliding members, requiring multiple clamps to secure and release the different movements of various levers comprising the components of the positioning devices in order to effect the desired positioning. All of these devices are cumbersome to use, because of the multiple clamps or cams which must be operated in order to lock the different motions of the different parts in place. Since all of these parts and motions are separately locked or released, the manipulation of the components and the accurate positioning of the instrument, with which they are designed for use, requires a substantial amount of skill and experience.
An effort to reduce the complexity of operation of a spatial positioning implement for positioning an electrode in a precise manner is disclosed in the U.S. patent to Pfeiffer No. 3,196,875. This patent is directed to a manipulating device, which is slidably mounted on a carriage on a semi-circular track. The carriage may be moved to different positions along the track and rotated or tipped about the track. Once the location of the carriage has been selected, it is locked in place on the track by a threaded locking handle.
In the Pfeiffer device, the instrument itself is carried on the tip of an extension of an elongated rod, which is slidably and rotatably mounted in a bore through a split compressible sphere. The sphere is held in a clamp having a split through it, which may be drawn together or released by means of a clamping lever. When the clamping lever is released, a handle on the end of the positioning rod may be used to move the rod back and forth through the bore in the sphere, and to rotate it until the instrument is located in the desired position. Once this has been effected, clamp jaws are contracted by manipulation of a lock lever to squeeze the compressible sphere. This holds the sphere in place, so that it cannot be rotated. The sphere also compresses against the bore through it to prevent further rotation and sliding of the rod extending through it.
Thus, two different mechanisms are required in Pfeiffer to complete the positioning of the device; and two different clamping members must be operated in order to effect that positioning. Manipulation of the two together effects the proper position of the instrument. Then two separate operations by the person utilizing the positioning device are necessary to lock it into place, and, subsequently, to release it.
Accordingly, it is desirable to provide a positioning device capable of positioning an implement in a three-dimensional coordinate system quickly and accurately, and in which the position of the implement then may be secured by means of the operation of a single locking member or control member.